Alaska Floodplain and Erosion Mitigation Commission Act of 2005 - Establishes the Joint Federal-State Floodplain and Erosion Mitigation Commission for Alaska to study all matters relating to: (1) the feasibility of alternatives for flooding or erosion assistance; and (2) the development of a policy to guide infrastructure investments in the Alaska Native villages, cities, and boroughs that are most affected by flooding or erosion.
Directs the Secretary of the Interior to: (1) evaluate and prioritize specific flood and erosion circumstances that affect life and property in Alaska; and (2) examine the most cost-effective ways of carrying out flood and erosion control and mitigation solutions devised by the Commission for nine villages in the State identified in a specified Government Accountability Office report. Authorizes the Secretary to implement a solution by making a grant to the State government or a local government using the remainder of funds appropriated for flood and erosion control and mitigation solutions. Delineates factors to be considered in implementing such a solution. Sets the Federal share of the cost at 75 percent. Authorizes the Secretary to take any action necessary to mitigate the loss of structures and infrastructure from flood and erosion using the most cost-effective means practicable to provide the longest-term benefit.